Thermoelectric devices are active components that provide cooling and heating effects, and their physical properties are described as follows: The ends of two wires made of different thermoelectric materials are soldered together to constitute a continuous circuit. If the ends of the wires are at different temperatures, the circuit will produce a slight voltage difference. Such phenomenon of producing electric power from heat is called the Seebeck effect.
On the other hand, the phenomenon of producing coldness from electric power when power is supplied to the foregoing circuit is called the Peltier effect. The heat at one end is absorbed and the heat on the other end is produced. The Seebeck and Peltier effects are the basic principles of thermoelectric devices.
The thermoelectric material used for thermoelectric devices has the following three properties. Firstly, the electromotive force per degree of temperature difference of the thermoelectric material, which is called the thermoelectric power of the material at the joint between components, is high.
Secondly, the thermal conductivity of the thermoelectric material is low, because if heat is conducted too quick, too large, or too small, the temperature difference will not be detected easily.
Thirdly, the electrical conductivity of the thermoelectric material is high.
The thermoelectric material is divided into two types: the N-type and the P-type defined as follows. If a current flows from the cold contact point of a thermoelectric material of a thermoelectric device made according to the Seebeck effect to other sections of the thermoelectric material, such thermoelectric material is called an N-type thermoelectric material; if the current flows into the cold contact point, then it is called a P-type material. A pair comprised of a P-type material and an N-type material is called a couple.
To improve the thermoelectric conversion efficiency, the selection and manufacture of thermoelectric materials are very important. The common thermoelectric materials such as bismuth-selenide alloy and antimony telluride, etc. having high thermoelectric conversion efficiencies are extensively used in thermoelectric modules; and thermoelectric alloys having higher efficiency and more complicated compositions are being developed.
In addition, the factors such as the adhesive strength and the stability of material used in the manufacturing process also affect the efficiency and reliability of thermoelectric modules. Therefore, it is necessary to select a stable manufacturing process.
At present, most thermoelectric devices are made manually as disclosed in the U.S. Pat. Nos. 4,907,060, 4,946,511, and 5,006,178. The N-type and P-type thermoelectric materials are slid into cubes of about 1 cubic millimeter, and a manual clamping tool is used to put a cube between two ceramic plates with solder, and then an adhesive substance is heated to adhere the cube between the ceramic plates.
Further, a method of automatically fabricating a thermoelectric device disclosed in the U.S. Pat. No. 4,493,939 mainly uses a vacuum chunk to separately put the N-type and P-type materials into the container having a plurality of orifices, and then the container is placed on the substrate, and then the container with orifices is removed. Finally, the N-type and P-type materials are adhered to the substrate by using the soldering reflow.
The U.S. Pat. No. 4,902,648 disclosed a method for improving the yield of manufacturing thermoelectric devices. The invention mainly manufactures the electrodes first, and then places the N-type semiconductor and the P-type semiconductor separately onto the electrodes one at a time, and finally adheres the two electrodes.
The U.S. Pat. No. 6,232,542 disclosed another method of manufacturing thermoelectric devices. The invention forms grooves on two thermoelectric blocks by lithographic exposures, and then combines the blocks to produce the thermoelectric device.
The U.S. Pat. No. 5,837,929 further disclosed another technology of manufacturing thermoelectric devices. The invention places an N-type material on a semiconductor wafer, and implants the N-type thermoelectric material into a P-type semiconductor by diffusion to form an alternate thermoelectric couple, and then separates the P-type and N-type semiconductors by etching, and finally manufactures the electrodes by metal deposition.
The U.S. Pat. No. 5,064,476 further disclosed another method of manufacturing thermoelectric devices. The invention sticks a conductive protruded member onto a substrate, and then uses a structure such as a frame to place the thermoelectric material between two substrates.
The U.S. Pat. No. 5,856,210 further disclosed another method of manufacturing thermoelectric device. The invention places the N-type and P-type materials into a prepared partitioning object, and makes the metallic electrodes double-sided, and then removes the partitioning object. The partitioning object is an insulator for preventing short circuits and facilitating the installation of thermoelectric components.
In view of the description above, the prior-art thermoelectric devices and their manufacturing methods have the following shortcomings:
1. All thermoelectric materials and substrates have one-sided surface contact only, and thus the conductive effect is not good.
2. The heat conducted in a reverse direction and produced by the contact resistor between the thermoelectric materials and substrates is too high, which will affect thermal conduction effect.
3. Regardless of the manufacturing method, it is necessary to use an accessory frame for fixing the thermoelectric material, which will increase the level of difficulty for the manufacturing and increase the manufacturing cost.
4. In the manufacturing process, the thermoelectric material has to go through the alignment process. If there is a slight discrepancy, it will easily affect the reliability of the components, and thus will lower the stability of the component manufacturing process.